Gas boiler shroud/windshield

[Kev888]

Hello all, I've not posted for quite a while, not had time to brew for ages, but I'm hoping that may improve soon

Anyway, it looks like I'm going to have to downscale and convert to gas to make it viable to continue, and I've not had much to do with gas before. To improve gas efficiency and heating times I'm going to add a shroud to the boiler to guide warm gasses up the sides and stop wind blowing them away, and I wanted to run a couple of ideas past the more experienced gas users on here:

• I'm imagining that the shroud should have some sort of escape route at the top to allow it to draw gasses up around the boiler like a chimney, rather than create dead air around it.
• Also I'm thinking around 35mm clearance between boiler and shroud would be about right for a 430mm diameter boiler and a ~9kw burner.

If anyone disagrees or has suggestions on this then I'd be most keen to hear!

Cheers
Kev

[woblylegs]

kev ive just being setting a burner up. i looked at the metal stands but i really didn't like the look of them plus a bit breeze will blow the flame. i made a shroud out of bricks and mortar.
i used it yesterday for the first time and encountered a slight problem in that the flame was not spreading the total surface of the pan so wasn't heating fast enough which was easily remedied with 4 x four inch nails it raised the pan aprox. 1/4 inch enabling the flame to spread out. it worked well
when the chiller was in cooling it seemed to take an age to cool then i realised the the bricks were hot as hell and thus keeping the boiler hot! easy remedy again..... placed some sticks to lift the boiler an inch off them and bingo, cooled a treat ans stick didn't burn!
not pretty but very affective and cost all of £4 for two flag stones sorry for pic quality

[Kev888]

Thanks, those spacings give me some idea of whats needed.

Cheers
kev

[Collingwood]

Kev888,

I’ve been reading about rocket stoves used in developing countries to cook food using just a few handfuls of sticks and twigs. Been wondering if some of the principles could be used in homebrewing.

An important feature of institutional rocket stoves (ie. those used to prepare big pots of food for a whole village) is the use of a skirt (or shroud) on the outside of the pot to contain the hot combustion gases and channel them up the sides. This puts the pot sides to use as a heating surface thus greatly increasing the heating efficiency of the stove and reducing fuel consumption.

You are using gas instead of wood as a fuel, but the thermodynamic principle of the skirt is the same.

Aid agencies have done a lot of engineering work into the mathematical relationship between the diameter of the pot and the diameter of the skirt. This information can be found at this website: http://www.rocketstove.org/index.php/de ... -from-menu

This page has links to two PDF files and an spreadsheet. The spreadsheet has at the top a few basic parameters (in grey) such as pot circumference, pot height etc. Just key in the measurements of your pot and it will calculate the size of the piece of sheet steel needed to produce a skirt with the best gap for thermodynamic efficiency. (Edit: The web page says that you need Firefox web browser to access the spreadsheet. But it works fine for me using Internet Explorer 11 and XL).

The two PDFs are good to browse to get an idea of how rocket stoves work, or just look up the many YouTube videos (note that many rocket stoves don’t use a skirt – it is the big “institutional” rocket stoves you need to look for).

Couple of points I’ve considered when thinking about using a skirt to help boil wort.

(1) In order to extend the ball valve out the extra distance to get clear of the surrounding skirt, you are going to need a longer nipple or pipe extension.

(2) If using a weldless fitting for the drain tap, don’t have a silicone washer or O-ring on the outside of the pot – it would be burnt by the high heat rising up the side of the pot (catastrophic failure if full of hot wort). Same for the gasket inside your ball valve – if the valve gets too hot it could fail.

(3) Even with a O-ring on the inside there could be too much heat being conducted through the pot wall to the O-ring causing it to degrade and fail. I’d look at cutting vertical slot a few inches wide in the skirt to accommodate the valve. I’d bend the skirt metal in beneath the tap to shield it from the hot gases. And similarly, I’d bend in the vertical edges of the slot to keep the hot gases channelled against the pot.

(4) Consider having the height of the skirt much less than the height of the pot. Reason being that if you heat the pot wall area that is not in contact with wort you could cause severe scorching or burning of wort that splashes about during the boil. The heat might also burn out the pot metal from the sides (especially if aluminium). So I’d keep the skirt height well below the level of the wort; and never have the gas turned on and firing until you’ve filled the pot to above the level of the top of the skirt.

I agree with your thinking about leaving the top of the skirt/shroud open to allow hot combustion gases to vent. Closing off the top of the skirt could cause the gases to billow out underneath the pot and cause problems with oxygen starvation to the gas burner, or worse - burning the gas feed line.

Anyway, good luck with this project. I’m interested in seeing how you go. I’m guessing (hoping) you can reduce gas consumption by 50% using a skirt.

[Kev888]

Many thanks indeed for taking the time to post all this!

There are some excellent ideas there as well as useful facts on clearances. I hadn't even considered extending the skirt underneath or insulating it, but (if done properly to suit the gas burner) I'd imagine this could work very well indeed for me. The insulation could well be good enough to maintain mash temperatures in a BIAB setup too; my system will need to be portable but I could use lightweight vermiculite or similar.

I also like the idea of ducting the hot exhaust gasses to a chimney; could make it more pleasant to have them vented above the area I'd be working/stirring etc.

Much to consider, I'm already reassessing some of what I'd intended. Thanks once again!!

Cheers
Kev

[Aleman]

As I said eleswhere Well I Did This



This is my 150L copper . . . Note that it has a 3" center drain, So I needed an appropriate burner . . .enter a 400mm 11KW paella burner from Hamilton Gas products. Having used gas for several years before this, and Hamilton saying it will take 6-8 hours to get 130L of water to boiling I decide to make it a little more efficient by adding some insulation. Now Phil has some gas burners and insulated coppers, but these are insulated with something that came off of the space shuttle . . . no I'm not kidding!! . . . Well it was developed out of the space shuttle project . . .

So what is the cheapest insulation available, anyone considered hot air. . . We have loads of it escaping up the sides of the boiler doing nothing . . . what if we could create a blanket out of it? :hmm: . . . no heat would be lost from the wort to the hot air blanket, and we are using a waste product to do it. A quick google, and I came up with a heat shroud which creates an air gap of about an inch round the kettle, it has a rolled top that almost seals the shroud to the kettle. . . . After a trip to the local fabricator they came up with this



Well this is it in the dark with the shroud fitted and the burner doing it's stuff . . . Note that I was running it at 150mBar at that point . . . It actually runs at 50mBar.



And the good news is that at 50mBar . . . it took 40L or water from 25C to 78C in 25 minutes . . . which is much better than the 19KW 50L copper(s) could manage so I'm quite pleased . . . as it means that I will be saving gas.

One thing I have discovered since using it a few times is that the inside gets hot enough to caramelise any wort that splashes up onto the inside surface of the copper, so it's doing a damn good job at trapping all that waste heat. I can also turn the outer ring of the burner off once boiling and just use the inner one.

Since those pictures were taken I have fixed the burner into place, and fitted some big casters so that I can move it about.

[Kev888]

Ah, most interesting, many thanks. I'd seen some of your posts on your shroud before, but I'd only thought of it as letting more heat get at the sides of the kettle - I hadn't considered it also therefore preventing heat loss from the kettle, though its quite obvious now you mention it. Doh!

So probably theres a great deal of similarity but also a slight difference in principle between having the kettle in an enveloping chimney of hot exhaust gasses vs having it in more of a shroud of hot air, although if the shroud weren't completely sealed presumably a sort of middle-ground would occur.

I'd been intending the boiler to be used in BIAB, which would be a bit of a departure for me (if it works out). Presumably one could maintain mash temperature almost indefinitely via a gentle hot air shroud, which did little more than remove any temperature gradient between the kettle and outside world. That would seem much better than trying to make up for losses by pumping more heat back into the mash through the base alone, risking denaturing the enzymes. I suppose the addition of an exterior skin of vermiculite would also help reduce losses, but whether it would gain very much for the added thickness I'm not sure.

In terms of design, do you think its okay to have the shroud permanently fixed in place, or can you see any need for it to be removable?

Many thanks,
Kev

[Collingwood]

There is a commercially available product available from US company Home Brew Tools. Its called The Heat Guide and sells for US$59 + shipping.

Link: http://www.homebrewtools.com/home

Its designed for use on a keg kettle and uses a series of flat metal panels to form a 'shield' (shroud, skirt) around the outside of the keg. Some interesting tests and performance analysis on the web site too. Thought it might be useful as a source of ideas.

Steve

[Kev888]

Looks like another possibility, thanks.

Cheers
Kev

[Jocky]

I'm looking at doing something similar for boiling outdoors in winter or when windy. My major concern is what will happen to the ball valve on the side of the boiler - I don't want it to get melted. I wondered whether if I created a shroud that I could create a shield around the valve too to avoid problems.

[Aleman]

Mine uses a long 1/2" BSPP nipple.

Two flange nuts seal the pot, then another flange nut on the inside against the shroud, and finally the female ball valve seals on the outside.

I did think about enclosing it an a short piece of 2" pipe to prevent excessive caramelisation, but so far it does not appear to be an issue.

[Jocky]

Ah, so the valve is on the outside of the shroud? That makes sense now.

[Collingwood]

[quote="Jocky"]I'm looking at doing something similar for boiling outdoors in winter or when windy. My major concern is what will happen to the ball valve on the side of the boiler - I don't want it to get melted. I wondered whether if I created a shroud that I could create a shield around the valve too to avoid problems.[/quote]

One solution that came to mind was to put the 'shroud' on the inside of the pot, so to speak. That is, attach a large diameter, open-ended stainless tube or pipe up the centre of the boil pot. Hot combustion gases rising up the tube would heat the inner sides of the tube, and the heat would be transferred to the wort on the other side of the tube wall (sort of turns the wort into a liquid donut in shape).

This configuration would provide a smaller additional heating surface compared to an outside shroud which uses the pot circumference, but I think more than enough to quicken time-to-boil and significantly reduce gas consumption. And with this configuration you could leave the valve in the normal position on the outside of the pot.

Just a thought.

[Kev888]

That would be an interesting idea, too. For myself, I think I'll stick with the external shroud, as I particularly like the idea that heating the air around the outside of the pot also prevents any heat loss from the sides.

I'm now thinking perhaps a two-mode setup would be appropriate for BIAB; one with an opening or chimney at the top for heating/boiling as normal, and another with the chimney/outlet closed and just enough heat to keep the air blanket warm for mashing without heat loss.

Cheers
kev

[Kev888]

Hmm, I was thinking of making the shroud out of aluminium to be lightweight and portable, but I happened across this attempt at a burner wind shield made with aluminium:

Okay, so my kettle shroud would be further from the flames unless they spread out more than I expect under the pot, but even so I'm not sure that I want to risk the cost of alu sheet to find it does anything even vaguely like that...

A quick google suggests aluminium melts at around 660C. By the looks of it, this shield wasn't quite melting, but had softened to the point where it was probably not too far off, so presumably its roughly around 600C at the edges of the burner flame. Not sure what its likely to be within a boiler shroud but I'd guess if the flames were almost reaching the pot edges it may be wise to assume it could be still something fairly serious.

The 'maximum oxidation service temperature' for stainless depends on the grade but the common ones are above 800C, which looks a lot better - though sadly stainless is neither cheap nor especially lightweight. Galvanised steel would be another potentially good option and much cheaper, but I'm not really sure enough of the temperature it will experience to be confident in choosing it; apparently it isn't recommended for continuous use above 200-250C or short term above 350C, due to it peeling/cracking over time. I don't really want to use plain/mild steel though, as to stand any chance of being lightweight it will be thin and so rust will eat through it quite quickly; perhaps I could paint it with heat resistant paint but I struggle to trust it..

Cheers
kev